LinkedIn had filed to go public but not yet made its stock market debut. Rumors were rife that Zynga, Yelp and Facebook were poised to do the same.

Today, professional networking site LinkedIn holds the 69th spot in the annual rankings, which compare Silicon Valley's public companies by revenue. Zynga, the social gaming company whose business is tied symbiotically to Facebook's, sits at No. 48.

And while Yelp didn't qualify for this year's SV150 because it didn't go public until March, its $83.3 million in 2011 revenue would have juuuust let it squeak into the bottom of this year's list.

But Facebook -- now just weeks away from launching the tech industry's most anticipated IPO since Google's (GOOG) -- figures to start playing with the valley's big boys and girls immediately upon getting into the public company game.

Had it been public last year, Facebook's sales of $3.7 billion would have let it debut on the list at No. 25 -- ahead of such stalwart names as Netflix (NFLX) and Salesforce.com.

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And when Facebook's 2012 revenues are tallied, the company almost certainly will rank even higher on next year's list, given its 85 percent growth rate between 2010 and 2011.

Analysts surveyed for this story estimate the Menlo Park social network could notch as much as $6.7 billion in revenue, a number that would put it around No. 11 on this year's list.

"I see it as a once-a-decade kind of company," said Bo Brustkern, founder of Denver-based Arcstone Partners. Using Google as a model, Brustkern estimates that Facebook will hit $12 billion in revenues next year and is worth $137 billion, based on its ability to dominate and redefine the way marketers reach people online.

Once Facebook goes public, the parade of social media IPOs likely will slow. Big-name social networks like Twitter and Pinterest are months, if not years, from needing to go public, most experts say, given the gobs of money venture capitalists have been throwing at them.

The next wave of valley stock launches may well be made by less-sexy enterprise software companies like Palo Alto Networks, which filed plans earlier this month for a $175 million offering. The Santa Clara-based maker of network security products reported $119 million in fiscal year 2011 revenues, which would have placed it 142nd on this year's list.

But Victor Shum, a tech attorney with Jeffer, Mangels, Butler & Mitchell in San Francisco, expects social media companies will continue to invade the ranks of the valley's top grossers over time.

For one thing, Shum said, the ever-growing numbers of iPhone and Android users will continue to swell traffic for LinkedIn, Yelp, Facebook and the like. He also noted that the amount of money and resources needed to build a social media company is paltry compared to, say, what it costs a biotech company to get a new cancer drug through the clinical and regulatory pipelines.

Shum thinks even "companies that are basically app makers" will have a path to the public markets, given Zynga's $1 billion IPO and the even more eye-popping $1 billion Facebook just spent to acquire photo-sharing service Instagram.

Such a trend, he said, reflects the valley's ever-shifting nature, as innovation continually pushes new companies to the top -- and topples old ones.

"Ten years ago, Palm was the No. 1 smartphone," he said. "They got creamed by BlackBerry, and look what's happening to BlackBerry now. The speed at which companies can succeed and collapse is phenomenal these days."

Facebook's IPO, he said, will only accelerate that trend.

"Once it goes public, a lot of people who've worked very hard are going to get recognized financially for their contributions," he said. "And they'll maybe go out and start the next big thing."

Contact Peter Delevett at 408-271-3638. Follow him at Twitter.com/mercwiretap.

BILLIONS AND BILLIONS

Estimates of how much revenue Facebook may tally this year vary, but they all include a lot of zeros:$5.4 billion -- PrivCo$6.2 billion -- Social Internet Fund$6.7 billion -- Arcstone Partners